The proposed research will study a major aspect of the toxicology of airborne inert particles: the effects of these particles on the function of alveolar macrophages. Inert particles in sizes comparable to those that reach the alveolar surface from inhaled air will be studied for effects on the activity of cultured rabbit alveolar macrophages. Special attention will be given to the ways in which these particles are taken up by the cells and their influence on the cell. Included will be studies of cytoxicity and determination of how particle load affects the ability of alveolar macrophage to endocytose soluble and particulate protein. Factors such as the ability to bind cytophilic antibody and to stimulate antibody production by means of cell bound antigen, will be considered. Also included will be a comparison of the endocytic activity of alveolar macrophages with that of peritoneal macrophages and an effort to distinguish the possible different energy requirements of phagocytosis, pinocytosis and micropinocytosis.